1. Field of the Invention
The present invention relates to a water-in-oil emulsion adhesive which can be used particularly favorably for papers.
2. Description of the Related Art
Booklet production and sealed document production are garnering much attention as methods for adding value to paper having images formed thereon. For example, in direct-mail advertising and the like, so-called self-mailers in which the paper is folded to form an envelope are now being used.
In order to enable a booklet or sealed document of an arbitrary size and shape to be prepared automatically in an in-line process, by using a post-processing device (finisher) such as a sealed document production device or booklet production device following completion of printing, issues that must be addressed include (1) the drying properties of the adhesive upon standing, (2) the storage stability, and (3) the ability to achieve adhesion in a short period of time.
In other words, booklet production and sealed document production may not necessarily be applications that are performed with high frequency, and therefore there is a possibility that the adhesive may be left to stand for a long period in an unsealed state inside a machine. Accordingly, if the adhesive dries or solidifies during standing in an open space, then unsatisfactory application of the adhesive occurs.
Further, if separation or degeneration or the like of the adhesive occurs during standing, then unsatisfactory application of the adhesive and poor adhesion and the like tend to occur.
Moreover, following application of the adhesive to the paper and subsequent bonding, the paper must be transported, and therefore the adhesive must dry quickly following application, and bond within a short time period.
Examples of known adhesives for paper include aqueous adhesives containing a water-soluble polymer such as starch, polyvinyl alcohol (PVA) or polyvinyl acetate dissolved in water. Among aqueous adhesives, PVA has a high level of safety, and exhibits favorable workability and adhesive performance, and is therefore widely used. Patent Documents 1 to 3 disclose aqueous adhesives that use PVA.
In order to shorten the adhesion time, the use of hot melt adhesives and active energy beam-curable adhesives and the like is also known, and in such cases, the adhesion time is shortened by the application of energy, either by heating or by irradiation with an active energy beam, following application of the adhesive. Patent Document 4 discloses a bookbinding device that uses a hot melt adhesive to perform bookbinding.